1. Field of the Invention
The present invention relates generally to a method and a system for measuring three-dimensional displacement of a mass. More specifically, the invention relates to a method and a system suitable for measuring three-dimensional displacement of a discontinuous surface, such as a crack in a rock or a natural joint and so forth.
2. Description of the Related Art
Conventionally, in fields of mechanical engineering, civil engineering and so forth, a non-contact type distance measuring equipment, such as a laser type displacement gauge, or a contact type displacement gauge employing a differential transformer and so forth are used practically. Namely, this measuring equipment performed high precision measurement of the displacement of a mass as an object of measurement (hereinafter referred to as a measuring object) as a relative displacement from a reference portion where various displacement gauges are placed.
Also, particularly in the field of civil engineering and mining, or in the field of geophysics, measurement of the displacement of a foundation, such as a rock, is performed for appropriately evaluating behavior of rock or crust. As a method for measuring the displacement of the foundation, a measuring method employing an extensometer is typically employed. Namely, this method makes analysis of the displacement of the foundation by setting a fixed measuring point within a bore hole formed in the foundation, such as the rock, and measuring a variation of a distance between the fixed measuring point and a measuring point located at the opening end of the bore hole on the earth by means of the extensometer.
However, when the displacement of the mass is measured by the conventional measuring system and method, the relative displacement from the reference portion where the displacement gauge is located is merely measured as a linear relative displacement. Therefore, in order to measure the three dimensional displacement of the mass, displacement measurements are by means of a plurality of measuring apparatus which are arranged three-dimensionally. This makes installation of the measuring apparatuses and collection of measured data complicated.
Furthermore, in particular when three-dimensional behavior of the foundation is to be evaluated by the extensometer, since the measuring method employing the extensometer permits only evaluation of relative linear displacement between two measuring points along an axis of the bore hole, it is inherent to three-dimensionally arrange a plurality of bore holes to perform multi-axes and multi-point measurement for three-dimensional evaluation. In addition, in the method, it is not possible to instantly detect the behavior of a discontinuous surface, such as a crack of the rock, a natural joint and or so forth, which sensitively reflects variations of the stress condition of the foundation.
Namely, in the conventional method employing the extensometer, a problem is encountered by requiring a huge amount of experiments for performing multi-axis and multi-point measurement for evaluating the three-dimensional behavior of the foundation. Also, the conventional method cannot make analysis of the behavior by specifying the discontinuous surface, but rather unitarily evaluates deformation of the discontinuous surface associating with variation of the stress condition in the foundation and displacement of the foundation as a continuous body. Therefore, it is not possible to perform evaluation by specifying deformation of the discontinuous surface primarily determining deformation of the foundation. In the prior art, a further problem is encountered in the impossibility of proper evaluation of the relationship between the behavior of the overall foundation and the behavior of the discontinuous surface, deformation direction, and deformation magnitude.